• 한국환경보건학회지
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• 제44권3호
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• pp.238-243
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• 2018

Objectives: The purpose of this study was to determine skin adhesion rate of children's modeling clay for exposure assessment. Methods: Children's modeling clays were classified into 10 categories as PVA clay, PVA soft clay, starch-based clay, foam clay, rubber clay, oil clay, muddy clay, terra clay, paper clay and slime. A total of 26 children's clay goods was selected. Moisture content (%) and hardness of clays were measured. Five adults aged 20 to 25were recruited for experiment. Gravimetric difference of modeling clay was determined after 3 minutes playing time. Skin adhesion rate ($g/min/cm^2$) was estimated bythe amount of skin adhesion per minute (g/min) and each individual's palm surface area ($cm^2$). Results: Twenty four of the 26 children's modeling clay products were adhesive to skins. Two products of foam and rubber clay were not adhered to skin. For the 24 products, the average skin adhesion rate was $5.5{\times}10^{-4}{\pm}4.0{\times}10^{-4}g/min/cm^2$. The highest skin adhesion rate was $1.3{\times}10^{-3}{\pm}4.4{\times}10^{-4}g/min/cm^2$ for paper clay. The lowest skin adhesion rate was $4.6{\times}10^{-5}{\pm}1.1{\times}10^{-4}g/min/cm^2$ for oil clay. The skin adhesion rate was increased with increase of moisture content. Adhesion rates of some clays were varied by person and testing trials. Conclusion: The study determined skin adhesion rate of children's modeling clay. The adhesion rate is useful for exposure and risk assessments and setting safety guideline to protect children's health.

• 한국CDE학회논문집
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• 제4권1호
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• pp.12-18
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• 1999

A deformable non-Uniform Rational B-Spline (NURBS) based volume is programed for the force reflecting exoskeleton haptic device. In this work, a direct free form deformation (DFFD) technique is applied for the realistic manipulation. In order to implement the real-time deformation, a nodal mapping technique is used to connect points on the virtual object with the NURBS volume. This geometric modeling technique is ideally incorporated with the force reflecting haptic device as a virtual interface. The results in this work introduce details for the complete set-up for the realistic virtual clay modeling task with force feedback. The force reflecting exoskeleton haptic manipulator, coupled with a supporting PUMA 560 manipulator and the virtual clay model are integrated with the graphics display, and results show that the force feedback from the realistic physically based virtual environment can greately enhance the sense of immersion.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1047-1059
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• 2019

This work describes the development of a numerical module with a multiphysics structure to simulate the thermo-hydro-chemo-mechanical behavior of compacted bentonites. First, the conceptual model, based on the state-of-the-art formulation for clay-based engineered barriers in deep geological repositories, is described. Second, the advantages of multiphysics-based modules are highlighted. Then, the guidelines to develop a code using such tools are outlined, presenting an example of implementation. Finally, the simulation of three tests that illustrate the behavior of compacted bentonites assesses the scope of the developed code. The satisfactory results obtained, and the relative simplicity of implementation, show the opportunity of the modeling strategy proposed.

• 소성∙가공
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• 제1권1호
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• pp.5-10
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• 1992

• 한국환경보건학회지
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• 제48권1호
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• pp.36-43
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• 2022

Background: Preservatives are used to prevent product deterioration in modeling clay. Parabens, a representative preservative, have been found to be endocrine disruptors and cause skin irritation and allergic reactions. Isothiazolinone preservatives can be irritating to the skin, respiratory tract, and eyes. Thorough investigation and regulation of clay are necessary because clay is marketed to children, who are more sensitive to the toxic effect of chemicals. Objectives: In this study, the presence of 16 preservatives was analyzed in modeling clay and the results were compared with current standards. Methods: A total of 200 samples were collected from 28 children's clay products sold in South Korea (13 from Korea and 15 imported from overseas). Twelve preservatives, such as parabens, were analyzed using high-performance liquid chromatography (HPLC). Isothiazolinone preservatives (chloromethylisothiazolinone; CMIT, methylisothiazolinone; MIT, octylisothiazolinone; OIT, and benzisothiazolinone; BIT) were analyzed using ultra performance liquid chromatography-tandem mass spectrometery (UPLC-MS/MS). Results: Dehydroacetic acid (DHA) was detected the most in the clays at 51.50% (103 cases) detection; 38 cases (median 190.42 ㎍/g) in Korean products and 65 cases (median 169.62 ㎍/g) in Chinese products. CMIT, which is prohibited in Korea, was detected in 14 (median 16.28 ㎍/g) Chinese products. OIT, which has a chemical structure similar to CMIT was found in 28 (median 68.38 ㎍/g) samples in Korean products. Conclusions: The use of CMIT and MIT in children's products is prohibited in Korea and the European Union (EU). The detection of CMIT in Chinese clay products suggests that management is necessary for imported products. It is necessary to review the safety and regulatory status for OIT because OIT was used as a substitute for CMIT and MIT in Korean products.

• 자원환경지질
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• 제43권2호
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• pp.185-196
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• 2010

열수변질에 의한 점토맥이 존재하는 사면 발생시 사면의 안전성에 영향을 미치는 것으로 알려져 있다. 파괴면의 형성 위치에 따라 접촉면 조건과 비접촉면 조건으로 분류하여 점토맥의 점착력, 내부마찰각, 방향성, 지하수위, 강우강도, 강우 지속시간 등의 인자에 따라 점토맥이 사면 안전율에 미치는 영향을 수치 모델링 연구를 통해 조사하였다. 지반 정수가 클수록 사면 안전율이 증가하였다. 사면 내 지히수위가 상승하면 사면 안전율이 감소하는 것을 확인하였다. 다양한 토양에 대한 강우 침투 모델링 결과 이질토는 강우강도에 따라 다양한 지하수위 발달 경향을 보인다. 반면에 사질토는 빠른 배수로 인해 지하수위의 상승이 거의 나타나지 않았다. 따라서 점토맥이 존재하는 사면에서 사질토는 이질토에 비해 사면 안전율에 미치는 영향이 적었다.

• Geomechanics and Engineering
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• 제10권6호
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• pp.827-836
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• 2016

The rate of softening is an important factor to determine whether the failure occurs along localized shear band or in a more diffused manner. In this paper, strength loss and softening rate effect depending on sensitivity are investigated for weakly cemented clays, for both artificially cemented high plasticity San Francisco Bay Mud and low plasticity Yolo Loam. Destructuration and softening behavior for weakly cemented sensitive clays are demonstrated and discussed through multiple vane shear tests. Artificial sensitive clays are prepared in the laboratory for physical modeling or constitutive modeling using a small amount of cement (2 to 5%) with controlled initial water content and curing period. Through test results, shear band thickness is theoretically computed and the rate of softening is represented as a newly introduced parameter, ${\omega}_{80%}$. Consequently, it is found that the softening rate increases with sensitivity for weakly cemented sensitive clays. Increased softening rate represents faster strength loss to residual state and faster minimizing of shear band thickness. Uncemented clay has very low softening rate to 80% strength drop. Also, it is found that higher brittleness index ($I_b$) relatively shows faster softening rate. The result would be beneficial to study of physical modeling for sensitive clays in that artificially constructed high sensitivity (up to $S_t=23$) clay exhibits faster strain softening, which results in localized shear band failure once it is remolded.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.232-239
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• 2005

Recently geosynthetics that can be constructed on soft ground have been used for reinforcement and separation in various ways. Through laboratory model tests and numerical analysis, in this study, estimated the suitability of cable elements and appropriate input factors considering loading effect in modeling of geosynthetics. First, in laboratory model tests, geosynthetics were constructed on the clay, and covered with the thickness, 7.5cm of sand mat. And then static and dynamic model tests were performed measuring loading, settlement, ground lateral displacement, and displacements of geosynthetics, but, for cyclic loading, bearing capacity increased linearly with stiff slop because cyclic loading with constant cyclic pressure compacted the ground. Numerical analysis were performed with FLAC 4.0 2D using Mohr-Coulomb and Modified Cam-Clay models, and they compared with the results of model tests. Cable elements of FLAC in modeling geosynthetics couldn't consider the characteristics of geosynthetics that increase shear strength between geosynthetics and clay according to the loading increase. Therefore, in this study, appropriate equation that can consider loading effects in Cable elements was proposed by Case Study.

• Geomechanics and Engineering
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• 제14권1호
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• pp.43-50
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• 2018

Applicability of constructing piled raft foundations on soft clay has been given attention in recent years. Lack of sufficient stiffness for soil and thus excessive settlements to allow higher contribution of piles is the major concern in this regard. This paper presents a numerical investigation of performance of piled-raft foundations on soft clay with focusing on a case study. A 3D FEM numerical model is developed using ABAQUS. The model was calibrated by comparing physical and numerical modeling results of other researchers. Then the possibility of using piled-raft system in construction of foundation for a water storage tank in Sarbandar, Iran is assessed. Soil strength parameters in the numerical model were calibrated using the instrumentation data of a heavily instrumented preloading project at the construction site. The results indicate that choosing the proper combination of length and spacing for piles can lead to acceptable differential and total settlements while a high percentage of total bearing capacity of piles can be mobilized, which is an efficient solution for the project. Overall, the construction of piled-rafts on soft clays is promising as long as the total settlement of the structure is not imposing restrictions such as the common 25 mm allowable settlement. But instead, if higher allowable settlements are adopted, for example in the case of rigid steel tanks, the method shall be applicable with considerable cost savings.

• 한국지반공학회논문집
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• 제15권6호
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• pp.17-28
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• 1999

본 연구에서는 자연점토의 압밀에 대한 변형률속도의 영향을 해석하기 위하여 비선형 점탄소성 모델을 제안하였다. 연약지반의 점소성 거동은 유일한 유효응력-변형률-변형률속도 (equation omitted)의 관계식으로부터 구할 수 있다. Berthierville 점토에 대한 크리프실험, 다단계 하중실험, Relaxation실험과 같은 실내실험결과와 수치해석결과를 비교하였다. 제안된 점탄소성 모델을 사용하여 자연점토의 압밀거동을 비교적 정확히 예측할 수 있다.